We study the star formation quenching mechanism in cluster galaxies by fitting the spectral energy distribution (SED) of the Herschel Reference Survey, a complete volume-limited K-band-selected ...sample of nearby galaxies including objects in different density regions, from the core of the Virgo cluster to the general field. The SEDs of the target galaxies were fitted using the CIGALE SED modelling code. The truncated activity of cluster galaxies was parametrised using a specific star formation history with two free parameters, the quenching age QA and the quenching factor QF. These two parameters are crucial for the identification of the quenching mechanism, which acts on long timescales when starvation processes are at work, but is rapid and efficient when ram pressure occurs. To be sensitive to an abrupt and recent variation of the star formation activity, we combined twenty photometric bands in the UV to far-infrared in a new way with three age-sensitive Balmer line absorption indices extracted from available medium-resolution (R ~ 1000) integrated spectroscopy and with Hα narrow-band imaging data. The use of a truncated star formation history significantly increases the quality of the fit in HI-deficient galaxies of the sample, that is to say, in those objects whose atomic gas content has been removed during the interaction with the hostile cluster environment. The typical quenching age of the perturbed late-type galaxies is QA ≲ 300 Myr whenever the activity of star formation is reduced by 50% < QF ≤ 80% and QA ≲ 500 Myr for QF > 80%, while that of the quiescent early-type objects is QA ≃ 1−3 Gyr. The fraction of late-type galaxies with a star formation activity reduced by QF > 80% and with an HI-deficiency parameter HI−def > 0.4 drops by a factor of ~5 from the inner half virial radius of the Virgo cluster (R/Rvir < 0.5), where the hot diffuse X-ray emitting gas of the cluster is located, to the outer regions (R/Rvir > 4). The efficient quenching of the star formation activity observed in Virgo suggests that the dominant stripping process is ram pressure. We discuss the implication of this result in the cosmological context of galaxy evolution.
We investigate the relationship between stellar mass, metallicity and gas content for a magnitude- and volume-limited sample of 260 nearby late-type galaxies in different environments, from isolated ...galaxies to Virgo cluster members. We derive oxygen abundance estimates using new integrated, drift-scan optical spectroscopy and the base metallicity calibrations of Kewley & Ellison (2008, ApJ, 681, 1183). Combining these measurements with ultraviolet to near-infrared photometry and Hi 21 cm line observations, we examine the relations between stellar mass, metallicity, gas mass fraction and star formation rate. We find that, at fixed stellar mass, galaxies with lower gas fractions typically also possess higher oxygen abundances. We also observe a relationship between gas fraction and metal content, whereby gas-poor galaxies are typically more metal-rich, and demonstrate that the removal of gas from the outskirts of spirals may increase the observed average metallicity by ~0.1 dex. Although some cluster galaxies are gas-deficient objects, statistically the stellar-mass metallicity relation is nearly invariant to the environment, in agreement with recent studies. These results indicate that internal evolutionary processes, rather than environmental effects, play a key role in shaping the stellar mass-metallicity relation. In addition, we present metallicity estimates based on observations of 478 nearby galaxies.
The transformations that take place in late‐type galaxies in the environment of rich clusters of galaxies at
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are reviewed. From the handful of late‐type galaxies that inhabit local clusters, whether they were formed in situ and survived as such, avoiding transformation or even destruction, or if they are newcomers that have recently fallen in from outside, we can learn an important lesson on the latest stages of galaxy evolution. We start by reviewing the observational scenario, covering the broadest possible stretch of the electromagnetic spectrum, from the gas tracers (radio and optical) to the star formation tracers (UV and optical), the old star tracers (near‐IR), and the dust (far‐IR). Strong emphasis is given to the three nearby, well‐studied clusters Virgo, A1367, and Coma, which are representative of different evolutionary stages, from unrelaxed and spiral‐rich (Virgo) to relaxed and spiral‐poor (Coma). We continue by providing a review of models of galaxy interactions that are relevant to clusters of galaxies. Prototypes of various mechanisms and processes are discussed, and their typical timescales are given in an appendix. Observations indicate the presence of healthy late‐type galaxies falling into nearby clusters individually or as part of massive groups. More rare are infalling galaxies belonging to compact groups, where significant preprocessing might take place. Once they have entered the cluster, they lose their gas and quench their star formation activity, becoming anemic. Observations and theory agree in indicating that the interaction with the intergalactic medium is responsible for the gas depletion. However, this process cannot be the origin of the cluster lenticular galaxy population. Physical and statistical properties of S0 galaxies in nearby clusters and at higher redshift indicate that they originate from spiral galaxies that have been transformed by gravitational interactions.
Osteoarthritis (OA) is a degenerative chronic disease affecting >300,000 million people around the world as of 2016. Symptomatic measures exist, but there are hardly any curative treatments ...available. Disruption of the cartilage homeostasis in favor of catabolism leads to cartilage destruction. ROS-macromolecular-induced damage is significantly greater in OA cartilage and OA is described as low-grade chronic systemic inflammation. This review aimed to assess the critical role of cartilage ageing and oxidative stress in the OA process, focusing in particular on NADPH oxidase and especially Nox4 involvement. With age, hypertrophic senescent cells with an altered redox cell profile accumulated. Chondrocytes are more sensitive to oxidant-mediators and the serum level of pro-inflammatory mediators increases. Age-related advanced glycation end products impact on extra cellular matrix (ECM) properties leading to the apoptosis of chondrocytes. A focus on NADPH oxidase-mediated-ROS signaling highlighted the very specific Nox4 isoform, which plays a role on the final common pathway targeting chondrocyte cells. IL-1β-mediated Nox4 stimulation induced an increase in the levels released by the chondrocyte of MMP-1 and MMP-13 proteins, which are involved in ECM degradation. In comparison with the other Nox isoforms, Nox4 remains unusual, since it is constitutively active, does not depend on cytosolic activator proteins and seems to generate H2O2 thanks to the specific conformation of the Nox4 E-loop. Nox4-induced ROS production appears an essential actor in the OA process and it could be relevant to focus on this target in the aim of discovering and developing new therapeutic strategies.
•Osteoarthritis is a form of low-grade chronic systemic inflammation.•Even small O2 metabolism modifications can have significant impact on chondrocytes.•Age-related hypertrophic senescent cells have an altered redox cell profile.•Nox could be the first ROS-producer acting as a trigger.•Nox4-induced ROS production is an interesting target for therapeutic strategies.
We report the detection of Hα trails behind three new intermediate-mass irregular galaxies in the NW outskirts of the nearby cluster of galaxies Abell 1656 (Coma). Hints that these galaxies possess ...an extended component were found in earlier, deeper Hα observations carried out with the Subaru telescope. However the lack of a simultaneous r-band exposure, together with the presence of strong stellar ghosts in the Subaru images, prevented us from quantifying the detections. We therefore devoted one full night of Hα observation to each of the three galaxies using the San Pedro Martir 2.1 m telescope. One-sided tails of Hα emission of 10–20 kpc projected size were detected, suggesting an ongoing ram pressure stripping event. We added these 3 new sources of extended ionized gas to the 12 previously found, NGC 4848, and NGC 4921 whose ram pressure stripping is certified by HI asymmetry. This brings the number sources with Hα trails to 17 gaseous tails out of 27 (63%) late-type galaxies (LTG) members of the Coma cluster with direct evidence of ram pressure stripping. The 27 LTG galaxies, among these the 17 with extended Hα tails, have kinematic properties that are different from the rest of the early-type galaxy population of the core of the Coma cluster, as they deviate in the phase-space diagram |ΔV|/σ versus r/R200.
We study the evolution of dwarf (L sub(H) < 10 super(9.6) L sub(H) unk) star-forming and quiescent galaxies in the Virgo Cluster by comparing their UV to radio centimetric properties to the ...predictions of multizone chemospectrophotometric models of galaxy evolution especially tuned to take into account the perturbations induced by the interaction with the cluster intergalactic medium. Our models simulate one or multiple ram pressure stripping events and galaxy starvation. Models predict that all star-forming dwarf galaxies entering the cluster for the first time loose most, if not all, of their atomic gas content, quenching on short timescales ( less than or equal to 150 Myr) their activity of star formation. These dwarf galaxies soon become red and quiescent, gas metal-rich objects with spectrophotometric and structural properties similar to those of dwarf ellipticals. Young, low-luminosity, high surface brightness star-forming galaxies such as late-type spirals and BCDs are probably the progenitors of relatively massive dwarf ellipticals, while it is likely that low surface brightness Magellanic irregulars evolve into very low surface brightness quiescent objects hardly detectable in ground-based imaging surveys. The small number of dwarf galaxies with physical properties intermediate between those of star-forming and quiescent systems is consistent with a rapid (<1 Gyr) transitional phase between the two dwarf galaxy populations. These results, combined with statistical considerations, are consistent with the idea that most of the dwarf ellipticals dominating the faint end of the Virgo luminosity function were initially star-forming systems, accreted by the cluster and stripped of their gas by one or subsequent ram pressure stripping events.
The Herschel Reference Survey is a complete volume-limited, K-band-selected sample of nearby objects including Virgo cluster and isolated objects. Using a recent compilation of HI and CO data for ...this sample we study the effects of the cluster environment on the molecular gas content of spiral galaxies. With the subsample of unperturbed field galaxies, we first identify the stellar mass as the scaling variable that traces the total molecular gas mass of galaxies better. We show that, on average, HI-deficient galaxies are significantly offset (4sigma) from the M(H sub(2)) vs. M sub(star) relation for HI-normal galaxies. We use the M(H sub(2)) vs. M sub(star) scaling relation to define the H sub(2)-deficiency parameter as the difference, on logarithmic scale, between the expected and observed molecular gas mass for a galaxy of given stellar mass. The H sub(2)-deficiency parameter shows a weak and scattered relation with the HI-deficiency parameter, here taken as a proxy for galaxy interactions with the surrounding cluster environment. We also show that, as for the atomic gas, the extent of the molecular disc decreases with increasing HI-deficiency. All together, these results show that cluster galaxies have, on average, a lower molecular gas content than similar objects in the field. Our analysis indicates that ram pressure stripping is the physical process responsible for this molecular gas deficiency. The slope of the H sub(2) - def vs. HI - def relation is less than unity, while the D(HI)/D(i) vs. HI - def relation is steeper than the D(CO)/D(i) vs. HI - def relation, thereby indicating that the molecular gas is removed less efficiently than the atomic gas. This result can be understood if the atomic gas is distributed on a relatively flat disc that is more extended than the stellar disc. It is thus less anchored to the gravitational potential well of the galaxy than the molecular gas phase, which is distributed on an exponential disc with a scalelength r sub(CO) Asymptotically = to 0.2r sub(24.5) (g). There is a clear trend between the NUV-i colour index, which is a proxy for the specific star formation activity, and the H sub(2)-deficiency parameter, which suggests that molecular gas removal quenches the activity of star formation. This causes galaxies migrate from the blue cloud to the green valley and, eventually, to the red sequence. The total gas-consumption timescale of gas deficient cluster galaxies is comparable to that of isolated, unperturbed systems. The total gas depletion timescale determined by considering the recycled fraction is T sub(gas,R) Asymptotically = to 3.0-3.3 Gyr, which is significantly larger than the typical timescale for total gas removal in a ram pressure stripping process, indicated by recent hydrodynamical simulations to be T sub(RP)Asympt otically = to 1.5 Gyr. The comparison of these timescales suggests that ram pressure, rather than a simple stop of the infall of pristine gas from the halo, will be the dominant process driving the future evolution of these cluster galaxies.
With the aim of quantifying the contribution of the environment on the evolution of galaxies at z = 0 we have used the DR7 catalogue of the Sloan Digital Sky Survey (SDSS) to reconstruct the 3-D ...distribution of 4132 galaxies in 420 square degrees of the Coma supercluster, containing two rich clusters (Coma and A1367), several groups, and many filamentary structures belonging to the “Great Wall”, at the approximate distance of 100 Mpc. At this distance the galaxy census is complete to Mi = –17.5 mag, i.e. ~4 mag fainter than M*. The morphological classification of galaxies into early- (ellipticals) and late-types (spirals) was carried out by inspection of individual SDSS images and spectra. The density around each galaxy was determined in cylinders of 1 Mpc radius and 1000 km s-1 half length. The color-luminosity relation was derived for galaxies in bins morphological type and in four thresholds of galaxy density-contrast, ranging from δ1,1000 ≤ 0 (UL = the cosmic web); 0 < δ1,1000 ≤ 4 (L = the loose groups); 4 < δ1,1000 ≤ 20 (H = the large groups and the cluster's outskirts) and δ1,1000 > 20 (UH = the cluster's cores). The fraction of early-type galaxies increases with the log of the over-density. A well defined “red sequence” composed of early-type galaxies exists in all environments at high luminosity, but it lacks of low luminosity (dwarf) galaxies in the lowest density environment. Conversely low luminosity isolated galaxies are predominantly of late-type. In other words the low luminosity end of the distribution is dominated by red dE galaxies in clusters and groups and by dwarf blue amorphous systems in the lowest density regions. At z = 0 we find evidence for strong evolution induced by the environment (Nurture). Transformations take place mostly at low luminosity when star forming dwarf galaxies inhabiting low density environments migrate into amorphous passive dwarf ellipticals in their infall into denser regions. The mechanism involves suppression of the star formation due to gas stripping, without significant mass growth, as proposed by Boselli et al. (2008a, ApJ, 674, 742). This process is more efficient and fast in ambients of increasing density. In the highest density environments (around clusters) the truncation of the star formation happens fast enough (few 100 Myr) to produce the signature of post-star-burst in galaxy spectra. PSB galaxies, that are in fact found significantly clustered around the largest dynamical units, represent the remnants of star forming isolated galaxies that had their star formation violently suppressed during their infall in clusters in the last 0.5–1.5 Gyrs, and the progenitors of future dEs.
Recent technological developments of multibeam echosounder systems (MBES) allow mapping of benthic habitats with unprecedented detail. MBES can now be employed in extremely shallow waters, ...challenging data acquisition (as these instruments were often designed for deeper waters) and data interpretation (honed on datasets with resolution sometimes orders of magnitude lower). With extremely high-resolution bathymetry and co-located backscatter data, it is now possible to map the spatial distribution of fine scale benthic habitats, even identifying the acoustic signatures of single sponges. In this context, it is necessary to understand which of the commonly used segmentation methods is best suited to account for such level of detail. At the same time, new sampling protocols for precisely geo-referenced ground truth data need to be developed to validate the benthic environmental classification. This study focuses on a dataset collected in a shallow (2–10 m deep) tidal channel of the Lagoon of Venice, Italy. Using 0.05-m and 0.2-m raster grids, we compared a range of classifications, both pixel-based and object-based approaches, including manual, Maximum Likelihood Classifier, Jenks Optimization clustering, textural analysis and Object Based Image Analysis. Through a comprehensive and accurately geo-referenced ground truth dataset, we were able to identify five different classes of the substrate composition, including sponges, mixed submerged aquatic vegetation, mixed detritic bottom (fine and coarse) and unconsolidated bare sediment. We computed estimates of accuracy (namely Overall, User, Producer Accuracies and the Kappa statistic) by cross tabulating predicted and reference instances. Overall, pixel based segmentations produced the highest accuracies and the accuracy assessment is strongly dependent on the number of classes chosen for the thematic output. Tidal channels in the Venice Lagoon are extremely important in terms of habitats and sediment distribution, particularly within the context of the new tidal barrier being built. However, they had remained largely unexplored until now, because of the surveying challenges. The application of this remote sensing approach, combined with targeted sampling, opens a new perspective in the monitoring of benthic habitats in view of a knowledge-based management of natural resources in shallow coastal areas.
•We explored poorly known and extremely shallow tidal channels with MBES.•We compare different segmentation approaches for VHR MBES data assessing their merits.•The study allowed the discovery of ecologically noteworthy biogenic features.•Methods investigated are repeatable and applicable to other geographical settings.
We report the detection of an Hα trail of 85 kpc projected length behind galaxy 2MASX J11443212+2006238 in the nearby cluster of galaxies Abell 1367. This galaxy was discovered to possess an extended ...component in earlier, deeper Hα observations carried out with the Subaru telescope. However, lying at the border of the Subaru field, the extended Hα tail was cut out, preventing the determination of its full extent. We fully map this extent here, albeit the shallower exposure.
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